Rheostat



(No Model.) a Sheets-Sheet 1.

J. P. B. PISKE. BHEQSTAT.

No. 518,236. Patented Apr. 17, 1894.

WTNESSES- 'WGMLW aw (No Model.) 3 Sheets-Sheet 2. J. P. B. FISKEL.

RHEOSTAT. No. 518,236. Paflsented Apr. 17; 1894.

-(No Model.)

' 3 Sheets-Sheet 3.

J. P. B. FISKE.

RHEOSTAT. No. 518,236. Patented Apr. 17, 1894.

.WIT ESSES- \/E TD aZJJMfi. f 5mb UNITED STATES ATENT OFFICE.

\ JONATHAN P. B. FISKE, OF LYNN, ASSIGNOR TO THE GENERAL ELECTRICCOMPANY, OF BOSTON, MASSACHUSETTS.

RH EQSTAT.

SPECIFICATION forming part of Letters Patent No. 518,236, dated April17,1894.

Application filed February 25, 1893. Serial No. 463,755. (No model.)

To aZZ whom it may concern.-

Beit known that I, JONATHAN P. B. FISKE, a citizen of the United States,residing at Lynn, county of Essex, and State of Massachusetts, haveinvented certain new and useful Improvements in Rheostats, of which thefollowing is a specification.

My invention relates to rheostats and it consists of certainimprovements in the several parts thereof, comprising, first, a novelconstruction of trays for supporting the resistance ribbon, and a trayholding frame so arranged that it is nearly impossible for shortcircuits to occur between the sections of the ribbon itself, or betweenthe ribbon and its supporting tray or the tray supporting frame. Theinvention also comprises improvements 1n current shifting devices whichpermit currents of large volume to be varied, without troublesomesparking between the contact plates and moving brushes.

The invention likewise comprises certain.

improvements in the contact brushes, possessing great advantages overthose which have hitherto been employed in the art.

The invention consists also in certain improvements whereby the capacityof the rheostat may be increased or diminished in definlte units veryeasily, and it relates, further, to specific details of construction, asreferred to hereinafter.

In the drawings, Figure 1 is a face View of a rheostat embodyingmyinVent-ion, showing the contact plates, the contact arm, the circul tconnections, and other details. Fig. 2 is a slde elevation, showing anumber of trays 1n their supporting frame, and'also the contact device,or switch. Fig. 3 is a plan view of one of the improved resistancecarrying trays. Fig. 4 is a section through the same, on line 4-4: Fig.3. Fig. 5 is a section on llne 5-5, Fig. 4- Fig. 6 is a side sectionalView showing the improved contact and are preventing devices. Fig. 7 isa detail illus trating the operation of one of the contact devices.

The rheostat proper consists of a tier of shallow, metal trays A whichsupport the resistance'ribbon B, wound back and forth in a zigzagmanner, and then laid from end to end of the tray alternately,connections being taken out at one end of the tray, at a, as many as maybe desired. The parallel sections of the resistance ribbon are insulatedfrom each other by asbestus, or other heat resisting insulating metal,though conductors possessing the prop- 6o erties of the alloy known asGerman silver are preferred. The resistance so disposed is held firmlyin position by clamping it between a half portion of the tray Amentioned,

and another corresponding half portion, as

shown in Fig. 4, the two halves meeting on a median plane and beingbolted together by bolts passing through the holes a as many as may berequired to give stiffness, according to the size of the tray. Theterminals a lead to the contact plates to be described hereinafter. Theopposite sides of the tray are united by ribs 0 which support theresistance ribbon and prevent its sagging when heated but leaves largeopen spaces through which air can freely circulate to carry 0% the heatwhen current is flowing. Insulation 0. is placed between the ribs andthe ribbon. The two half portions of the tray when united also leave anopen space between them at the end, as shown at a Fig. 2. These traysare carried by an outer metal frame D, as shown in Fig. 2, composed ofplates D D united by bolts E E, and clamping the trays between them, thetrays being supported at some dis.-

tance from each other by lugs 01, projecting from the frames D andleaving considerable space between the trays to assist convection of theheated air. The frame has feet 61 which may rest on the floor or besecured to a suitable support. In addition to the insulation between theresistance ribbon and the trays, already mentioned, other insulatingstrips or pieces a isolate the trays from the frame. With thisconstruction should an ac- 5 cidental contact exist between theresistance ribbon and one of the trays a complete shortcircuit by way ofthe frame is prevented, and possible injury is confined to theparticular tray in which the contact occurs. The trays r00 are so placedin the supporting frame that the terminals a of the adjacent trays leadout at opposite ends to terminal contact bolts H F, Fig. 2, and fromthese connection is made from as many trays as desired through suitableconductors to the contact plates G, Fig. 1, such connections, however,not being shown in this figure.

The contact mechanism is supported on a face plate or contact carryingplate H, Fig. 2. This plate may be made of hard wood, such as maple, andis supported on projections D Figs. 1 and 2, cast integral with theframe D and projecting through said plate II. The plate has a deepcircular groove in one or both faces, in which is placed a piece ofnoninflammable insulation, I, such as leatheroid. The projections D areon one side of and concentric with this insulating strip I, beingpreferably on the outside, while on the other side are a number ofplates K, only a portion of which can be seen through the cut-away partsat the upper left-hand side of Fig. 1. The number of these plates Kcorresponds with the number of contact plates G, which are secured tothe plates K by screws L, as shown, so as to be individually removable.The supporting projections or studs D extending from the frame Dconstitute magnetic poles which are energized by a coil M, shown insection in Fig. 6, which coil may be included in any electric circuitas, for instance, in series with the circuit 00 y, the magnetic circuitbeing completed through the frame D, central pillar D and the iron armsN N of the switch. The studs D are situated directly back of the gap orspace between the adjacent contact plates G, and are intended to blowout any are that may follow the traverse of the contact brush over theplates, in accordance with well known principles.

The brush carrying arm is composed of a middle portion N, and two endportions N, all of iron and insulated from each other by suitableinsulation a. They are clamped in alignment between side pieces 0, ofinsulation, such as leatheroid or vulcabeston, by bolts, as shown, andthe brushes at either end of the arm are connected by cables, as y, tothe external circuit in which flows the current which is to beregulated. The middle portion Nis pivoted upon a pin Pfixed in the frameD, and carries a pinion Q, or other means for rotating it on said pin tochange the position of the brushes, the contact plates Gbein g traversedby brushes carried at either end of the rotatable arm. These brushes arereally twin brushes possessing different characteristics. One iscomposed of copper and is indicated at B, Fig. 6. It consists of anumber of superposed copper laminae clamped in an inclined position, asshown, by a set screw S, in such manner that the end of each laminaerests upon the contact plate. This affords great current carryingcapacity. Ad-

jacent to the brush Ris another brush R,of carbon, of much less currentcarrying capacity than the brush R and in fact having a considerablyhigher resistance. The purpose of having two brushes is to preventarcing, the carbon brush being so supported, with relation to the copperbrush, that it is last to leave a segment G when the contact arm movesin either direction. The carbon brush may be wider than the copper brushto secure this result. If of the same width it may be placed at anarrower portion of the contact segments, or two carbon brushes may beplaced, one on either side of the copper brush, as shown in Fig. 7, togive the same result. The particular improve ment, however, upon whichstress is laid in the present invention consists in causing the brushesR and R to traverse separate portions of the contact plates G. Thisisimportant because there is always some slight sparking when a copperbrush leaves a contact segment which gives a slight roughness to thesurface. If the carbon brush were to traverse this roughened surface,but slight contact would be made. This would cause increased sparking atthe copper brush on account of the carbon brush failing to make goodenough contact to suppress the arc and the trouble would soon soexaggerate itself that the contact plates would be ruined. All this isobviated by arranging the brushes to ride on separate portions of thecontact plate surfaces, as indicated in Figs. 6 and 7. lhe carbon brushis retained in a suitable receptacle at the end of the arm N and ispressed into contact with the plate G by the spring T. Between themultiple magnetic poles D and the contact plates Gare interposed platesof 1n sulation U, Figs. 1 and 6,which may be leatheroid or othernon-combustible substance. Insulation U is also placed on the under sideof the arm. The insulation U prevents short circuits between the platesG and the poles D, and the insulation U prevents short circuits from thecontact plates G to the arm. Arcs formed between the contact plates Gare quickly disrupted by the magnetic field between the poles D and thearm, forming a part of the magnetic circuit. Such arcs destroy theinsulation in time, and it is therefore preferred to make suchinsulation in the form of removable insulating shields which can heslipped between the contact plates and the pole pieces. The dotted linesin thelowcr right-hand part of Fig. 1 indicate how these pieces may beremoved and inserted.

What I claim as new, and desire to secure by Letters Patent, is

1. A rheostat comprising a frame and a tier of removable trays supportedtherein, each tray containing a resistance coil, substantially asdescribed.

2. A rheostat comprisinga frame, a tier of removable trays supportedtherein, a resistance coil in each tray, and a series of contact opensides to permit free circulation of air,

substantially as set forth.

5. A rheostat comprising a frame, a tier of trays supported therein, aresistance coil in each tray, and insulation between said coil and thetray, substantially as described.

6. A tray for a rheostat having open sides with ribs extending acrossthem, substantially as set forth.

7. A tray for a rheostat composed of two portions meeting on a medianplane, substantially as described.

8. A tray for a rheostat composed of two similar port-ions meeting on amedian plane, each portion having an open side with ribs extendingacross it, substantially as set forth.

9. A resistance coil for a rheostat, comprising a removable conductorinclosed in a flat tray, such conductor being bent back and forth in thesame plane and having insulating strips inserted between adjacentlengths thereof, substantially as set forth.

10. The combination with the plates D having the lugs cl, of removabletrays A supported on said lugs, and resistance coils in said trays,substantially as described. Y

11. In a rheostat, the plate D having a plurality of studs D, and acentral pillar D a switch arm pivoted on said pillar and adapted toswing over said studs, and means for magnetizing said. parts,substantially as described.

12. In a rheostat, the plateD having aplurality of studs D, and acentral pillar D a helix surrounding said pillar, and a switch armpivoted on said pillar, substantially as set forth.

13. In a rheostat the plate D having aplurality of studs D',aninsulating face plate supported by said studs, and a series of contactplates carried by said insulating face plate, substantially asdescribed.

14. In a rheostat, the plate D having a-plurality of studs D, aninsulating face plate supported by said studs, a series of contactplates carried by said insulating face plate and projecting over saidstuds, and a sheet of insulation between the studs and the contactplates, substantially as set forth.

15. In a rheostat, the combination with magnetic spark rupturing polesand superposed contact plates, of a removable sheet of insulationinterposed between said poles and contact plates, substantially asdescribed.

16. In a rheostat, a switch arm provided with brushes of differentresistance moving in concentric arcs of diiferent radii, substantiallyas described.

17. In a rheostat, the combination with a series of contact plates, of aswitch arm carrying two brushes of different resistance, and arranged totraverse different portions of the contact plates, substantially as setforth.

18. In 'a rheostat, the combination with a series of contact plates, ofa switch arm carrying brushes of different resistance, and so arrangedthat in both directions of its motion the brush of higher resistance isthe last to leave the contact plates, substantially as described.

In testimony whereof I have hereunto set my hand this 23d day ofFebruary, 1893.

JONATHAN P. B. FISKE.

